Have you encountered these main reasons for the burning […]
Have you encountered these main reasons for the burning of refrigeration compressor windings?
The damage of the motor coil is mainly manifested in the destruction (short circuit) and open circuit of the stator winding insulation. After the stator winding is damaged, it is difficult to be found in time, which may eventually cause the winding to burn hardware machinery parts . After the winding is burnt, some phenomena or direct causes that caused the burn are covered, making it difficult to analyze and investigate the cause afterwards.
Factor 1: Abnormal load and stall
Motor load includes the load required for compressed gas and the load required to overcome mechanical friction. If the pressure ratio is too large, or the pressure difference is too large, the compression process will be more difficult; and the frictional resistance caused by the failure of lubrication and the blocking of the motor in extreme cases will greatly increase the motor load. Lubrication failure and increased friction resistance are the primary reasons for abnormal load.
Liquid return to dilute the lubricating oil, overheating of lubricating oil, deterioration of lubricating oil, and lack of oil, etc. will destroy normal lubrication and cause lubrication failure. Liquid return dilutes the lubricating oil, affecting the formation of the normal oil film on the friction surface, and even scouring the original oil film, increasing friction and wear.
Factor 2: Winding short circuit caused by metal shavings
Metal shavings in the windings are the main culprit for short circuits and low ground insulation. The sources of metal shavings include copper pipe shavings left during construction, welding slag, metal shavings dropped when the compressor is worn out and parts are damaged (such as broken valve plates).
For hermetic compressors (including hermetic scroll compressors), these metal chips or particles will fall on the windings.
For semi-hermetic compressors, some particles will flow in the system with gas and lubricating oil, and finally collect in the windings due to magnetism; and some metal chips (such as bearing wear and motor rotor and stator wear (sweeping)) will Fall directly on the winding. It is only a matter of time before a short circuit occurs after metal shavings have accumulated in the winding.
Factor 3: Winding short circuit caused by metal shavings
It is extremely important to correctly select the contactor according to the load. When using a single contactor, the contactor rated current must be greater than the motor nameplate current rating (RLA). At the same time, the contactor must be able to withstand the locked-rotor current of the motor. If there are other loads downstream of the contactor, such as motor fans, etc., they must also be considered.
When two contactors are used, the locked rotor rating of each contactor must be equal to or greater than the locked rotor rating of the compressor half winding.
Factor 4: Power phase loss and abnormal voltage
Abnormal voltage and phase loss can easily destroy any motor. The power supply voltage range cannot exceed ±10% of the rated voltage. The voltage unbalance between the three phases cannot exceed 5%. High-power motors must be powered independently to prevent low voltage when other high-power equipment on the same line starts and runs.
The motor power cord must be able to carry the rated current of the motor. If the compressor is running when a phase loss occurs, it will continue to run but there will be a large load current. The motor windings will quickly overheat, and the compressor will be thermally protected under normal circumstances.
Factor 5: insufficient cooling
Compressors with higher power are generally return air cooling type. The lower the evaporation temperature, the lower the system mass flow tends to be. When the evaporating temperature is very low (exceeding the manufacturer's specifications), the flow is not enough to cool the motor, and the motor will run at a higher temperature. Air-cooled compressors (generally no more than 10HP) have little dependence on return air, but have clear requirements for compressor ambient temperature and cooling air volume.
A large amount of refrigerant leakage will also reduce the mass flow of the system, and the cooling of the motor will also be affected. Some unattended refrigeration equipment often have to wait until the refrigeration effect is poor before discovering a large amount of refrigerant leakage.